Performance Analysis of Cooperative Spectrum Sharing for Cognitive Radio Networks Using Spatial Modulation at Secondary Users

In this paper, a new cooperative spectrum sharing protocol which avoids mutual interference between primary and secondary users by employing spatial modulation (SM) at the secondary transmitter (ST), is proposed for overlay cognitive radio networks. In the proposed protocol, ST cooperates with selective decode-and-forward (DF) relaying strategy to prevent error propagation. Primary transmitter (PT) exploits M-ary phase shift keying (M-PSK) modulation whereas ST utilizes SM (Nt transmit antennas and M- PSK). Since ST transmits PT's information by M-PSK symbols and its own information by antenna indexes, mutual interference at primary receiver (PR) and secondary receiver (SR) is removed. Upper bounds on the bit error probability (BEP) of the primary and secondary users are analytically derived and supported via computer simulation results which show that the proposed protocol significantly improves the bit error performance of both primary and secondary users compared to the non-cooperation case and the cooperative DF spectrum sharing protocol using superposition coding.